全文获取类型
收费全文 | 10375篇 |
免费 | 467篇 |
出版年
2020年 | 151篇 |
2019年 | 217篇 |
2018年 | 294篇 |
2017年 | 276篇 |
2016年 | 359篇 |
2015年 | 232篇 |
2014年 | 221篇 |
2013年 | 2851篇 |
2012年 | 297篇 |
2011年 | 341篇 |
2010年 | 316篇 |
2009年 | 291篇 |
2008年 | 260篇 |
2007年 | 251篇 |
2006年 | 212篇 |
2005年 | 151篇 |
2004年 | 139篇 |
2003年 | 125篇 |
2002年 | 137篇 |
2001年 | 195篇 |
2000年 | 141篇 |
1999年 | 158篇 |
1998年 | 119篇 |
1997年 | 115篇 |
1996年 | 114篇 |
1995年 | 91篇 |
1994年 | 89篇 |
1993年 | 105篇 |
1992年 | 112篇 |
1991年 | 86篇 |
1990年 | 85篇 |
1989年 | 86篇 |
1988年 | 83篇 |
1987年 | 100篇 |
1986年 | 87篇 |
1985年 | 110篇 |
1984年 | 111篇 |
1983年 | 140篇 |
1982年 | 109篇 |
1981年 | 112篇 |
1980年 | 115篇 |
1979年 | 96篇 |
1978年 | 103篇 |
1977年 | 116篇 |
1976年 | 96篇 |
1975年 | 110篇 |
1974年 | 67篇 |
1973年 | 61篇 |
1972年 | 63篇 |
1971年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The neutron activation analysis results from 30 glass samples were subjected to cluster analysis. The reliable localization of part of the medieval glass finds from Preslav enabled the evaluation of the variety of the production of a medieval glass workshop (ninth-tenth century), allowing conclusions to be made about the technological level of glass-making in Bulgaria during the Middle Ages. The work proved that NAA followed by cluster analysis is a successful approach to finding the local and chronological features of the investigated glasses. 相似文献
82.
AAS, FE and OES are each used in the analysis of thirteen samples of fragments of window glasses from three Catalan Gothic churches: Sta. Maria del Mar (Barcelona, Spain), Pedralbes Monastery (Barcelona, Spain) and Girona Cathedral (Spain). Two kinds of stained window glass are found. Special attention is paid to Co/Cu, Co/Ni and Cu/Ni ratios for blue glasses and Mn/Cu and Fe/Cu ratios for red glasses. 相似文献
83.
Gas liquid chromatography was used to analyse residues adhering to the inside of excavated potsherds from dated South African sites. The results suggested marine animal fat, possibly seal, had been cooked in the vessels. Fat of modern seals was baked and also analysed as a control sample. This gave similar results. The importance of seals in the prehistoric diet of the Southwestern Cape is supported by a large number of seal bones in the associated faunal material. 相似文献
84.
85.
86.
S.M. EVANS 《The Canadian geographer》1985,29(4):327-339
This paper describes some developments in the diffusion pattern of Hutterite colonies in North America. Today, there are more than 300 colonies distributed over the four western provinces of Canada and five states of the United States. The spatial behaviour of the three Hutterite clan-groups is compared, and responses by the sects to the repeal of the Alberta Communal Property Act in 1973 are assessed. Finally, changes in the rate of diffusion and the management of colony division are examined.
Cette communication décrit quelques développements dans la diffusion des colonies ďHutterites en Amérique du Nord. Aujourd'hui, il y a plus de 300 colonies dispersées dans les quatre provinces de ľoeust canadien et dans cinq états américains. Nous comparons le comportement spatial des trois groupes, ou clans, principaux ďHutterites et nous évaluons les réactions des sectes àľabrogation de la législation, de 1973, de la loi pourtant sur la possession en commun de propriétés Finalement. on examine le gérance de la division des colonies, et les changements dans leurs taux de diffusion. 相似文献
Cette communication décrit quelques développements dans la diffusion des colonies ďHutterites en Amérique du Nord. Aujourd'hui, il y a plus de 300 colonies dispersées dans les quatre provinces de ľoeust canadien et dans cinq états américains. Nous comparons le comportement spatial des trois groupes, ou clans, principaux ďHutterites et nous évaluons les réactions des sectes àľabrogation de la législation, de 1973, de la loi pourtant sur la possession en commun de propriétés Finalement. on examine le gérance de la division des colonies, et les changements dans leurs taux de diffusion. 相似文献
87.
88.
A number of investigations have been undertaken by the New South Wales Water Resources Commission to determine the regional and compound effects of large scale extractive industries on the stability of the Hunter River, New South Wales. Sedimentologic studies of bed material suggest that the Hunter River upstream of Denman has an armoured gravel bed that is immobile during regulated releases from Glenbawn Dam but is disrupted by moderate but less than bankfull flows. Annual bedloadyields have been computed by the bedload rating-flow duration technique for five river gauging stations. Approximate sand and gravel budgets for selected reaches of the Hunter River demonstrate that the present annual extraction rate from temporary sediment storages within the channel greatly exceeds the transport rate upstream of Denman and is approximately equal to the transport rate downstream of Denman. River degradation is imminent if extractive industries continue operating in the channel of the Hunter River 相似文献
89.
Nearshore water circulation and bar patterns at Coledale, New South Wales, were surveyed daily over thirty-six consecutive days, from 3 November to 8 December 1978, to identify sequences of changes that might occur in response to spring-to-spring tide cycles of fourteen days, changing barometric and wind conditions associated with the passage of anticyclonic weather systems across the coast, and day to day variation in the nearshore wave regime. During the survey the bar patterns tended to vary from transverse bars, through a composite arrangement incorporating longshore and transverse bars, to a longshore bar pattern as the tide changed from its spring to neap tide phase. However, this sequence was too brief to unequivocally establish variations in nearshore bar pattern that might be attributed to the fourteen day, spring-to-spring tide cycle. Nevertheless, morphologic changes occurring in response to wave regime fluctuation at Coledale were broadly in accord with studies from elsewhere by Dolan et al. (1979, 1982), and Clarke and Eliot (1982, 1983) in that bars and rips were systematically distributed along the beach. At Coledale, bars tended to relocate approximately 0.4 and 0.75 of the distance along the beach from its southern end. The preferred bar spacing closely matches hypothetical standing waves trapped between the headlands of the Coledale embayment. Temporally, the nearshore morphology is highly responsive to wave regime changes such that, as primary breaker heights decrease and remain below Hmax=1.0m, the bar pattern changes from longshore through mixed to transverse bar patterns within three to five days. On one occasion the bar pattern switched from a longshore to a transverse bar pattern within twenty-four hours. 相似文献
90.
Streamline analyses of mean monthly resultant surface winds over Australia are presented. Mean confluences represent either cyclone trajectories, or modal fronts. These analyses suggest that Australia's annual airstream climate is of two regimes: that of September to March inclusive, and April to August inclusive. The winter half-year is exemplified by a continental airstream source in southern Australia which diverges over virtually the entire continent. It continues into September and October, although dominating only the southern third to half of Australia, and is absent from November to March. During the summer half-year a new pattern emerges, with three maritime air stream sources represented over the continent: first, air from the Southern Ocean penetrates the south coast reaching its furthest northward extension from December to March inclusive; a second source originating over the Pacific Ocean dominates eastern and northern Australia; and a monsoon source originating over the Indian Ocean which flows overland affecting northern Western Australia. Two modal confluences are noted, one over northwestern Australia from November-February separating monsoon flow from that emanating from the east, and another extending from the west central coast east-southeastward to the southeast coast from November-March separating Southern Ocean air from that originating over the Pacific Ocean. 相似文献